In a control system, a programmable logic controller and a control network are used. The control network mainly performs transmission and reception of control signals and data between the programmable logic controller and a field device such as a remote input/output device.
The control system is often configured to include a plurality of control networks. The control networks constituting the control system are connected to each other by a relay station that relays data between the control networks. The relay station connects, via a network unit, each of the two or more control networks that are to be connected.
Generally, in such control systems, diagnosis information on the control networks can be acquired via the network unit connected to the control networks.
To acquire the diagnosis information, an engineering device needs to be connected explicitly, or in a visually understandable manner, to a device that is connected to a control network from which diagnosis information is to be acquired. This means that to acquire diagnosis information on a connection network, the engineering device needs to be directly connected to the device that is connected to the control network on which diagnosis information is to be acquired, or the engineering device needs to be connected a device that is connected to another control network separate from the control network on which diagnosis information is to be acquired; and a device connected to the control network on which diagnosis information is to be acquired needs to be explicitly, or clearly designated via the control network separate from the control network on which diagnosis information is to be acquired, thereby acquiring the diagnosis information from the designated device in remote control.
Patent Literature 1 and Patent Literature 2 disclose a method of acquiring a diagnosis information from an engineering device without explicitly designating the device that is connected to a control network on which diagnosis information is to be acquired.